Systemic lupus erythematosus (SLE) is a kind of autoimmune disease, which involves multiple organ systems of the body such as skin, joints, heart, lung, kidney, blood and brain, and is diffusely progressive, with remission and reccurence being occurred alternatively. Systemic lupus erythematosus mainly affects African-Caribbean, Asians and Hispanics, while having minor affection on Caucasian (the white race). According to Lupus Foundation of America, it is conservatively predicted that systemic lupus erythematosus affects 300,000 people in America. Under the estimation of Datamonitor Company, there are 2.2 million patients suffered from systemic lupus erythematosus merely in China, India and Mexico, wherein patients suffered from systemic lupus erythematosus in china are more than 1 million, which is the highest in the world. Since the initial symptoms of systemic lupus erythematosus are quite larvate, the actual amount of the patients may be far more than the current estimation. Thus there are strong demands on the diagnosis and treatment of SLE in clinic.
The cause of SLE is complicated and uncertain. It is not caused by a single factor, and may be related to various factors such as heredity, environment, sex hormone and immunity, etc. At present, it is widely acknowledged by the scientific community that pathogenesis of SLE is that, at the cellular level, the self-reaction B cell stays too long in peripheral tissues, and produces human autologous antigen, which causes autoimmunity. Therefore, if it is possible to inhibit the growth and proliferation of initial B cell, the SLE can be treated.
B Lymphocyte Stimulator (BLyS), also known as Tall-1(TNF and Apol related leukocyte expressed ligand 1), BAFF (B cell activating factor belonging to the TNF family), THANK (TNF homologues that activate apoptosis, NF-κB and JNK), belongs to tumor necrosis factor (TNF) family, and is a new cytokine firstly discovered and cloned by Hongbing Shu et al in 1999. As a co-stimulator of B Lymphocyte cell, BLyS can, in the presence of anti-IgM and IL-4, exclusively stimulate the proliferation and differentiation of B cell, and play a very important role in humoral immunity. And its over expression in the body is closely related to autoimmune disease.
Experiment in vitro shows that, after B cells are pre-activated by IgM, BLyS can induce B cells to massively proliferate and secrete large amount of IgM and IgA. However, for the B cells in rest period, this stimulation does not have obvious effect. Further study shows that, BLyS mainly acts on pre-B-lymphoid cells, immature B-lymphoid cells and activated lymphoid cells, while having no effect on plasmocyte, and lymphatic pluripotent stem cells. Like most cytokines, BLyS stimulates downstream signal transmission via the surface receptor of B cells. Many study groups confirmed that the receptors combined with BLyS are: receptor of B cell activating factor (BR3, BLyS receptor 3 or BAFF-R), transmembrane activator (transmembrane activator-1 and calcium modulator and cyclophilin ligand-interactor, TACI) and B cell maturation antigen (BCMA). This specificity determines that BLyS is a very good target for B cell antibody mediated autoimmunity diseases and lymphoma cancer.
It has been demonstrated in vivo and in vitro that the therapeutic antibody of anti-BLyS can effectively inhibit the growth of B cells, and the secretion of IgA and IgM, thereby achieving the effect of treating SLE (Edwards B M et al, The remarkable flexibility of the human antibody repertoire; isolation of over one thousand different antibodies to a single protein, BLyS. J Mol Biol. 2003 Nov. 14; 334(1):103-18; Baker K P et al, Generation and characterization of LymphoStat-B, a human monoclonal antibody that antagonizes the bioactivities of B lymphocyte stimulator. Arthritis Rheum. 2003 November; 48(11): 3253-65). Benlysta, an anti-BLyS antibody developed by US Human Genome Sciences Inc, becomes the first new medicament for SLE treatment in the past 60 years. Benlysta only aims at B cell stimulated by BLyS, and largely reduces the side effect during the therapy comparing to chemotherapy medicaments, therefore providing a safe and effective therapy for patients with SLE. Study and clinical application of targeted therapy against BLyS are developed rapidly in recent years, and most of the companies other than Human Genome Sciences Inc use fusion proteins modified on the base of BLyS or the receptor thereof. The US Genentech company developed medicament BR3-FC, Zymogenetics developed medicament TACI-FC, and AMGEN developed polypeptide-FC. In comparison with Benlysta, these medicaments have low specificity, weak binding force, relatively poor curative effect and stronger toxicity. The three medicaments are all stopped or terminated at clinical trial II. Therefore, antibody medicament of anti-BLyS is exactly the effective pharmaceutical treatment for this target.
Benlysta is produced by means of phage display library. And the disadvantages of phage display library are that: the pairing of heavy chains and light chains is thought to be artificial without in vivo selection (Greg Winter, et al., Making Antibodies by Phage Display Technology. Annual Review of Immunology Vol. 12: 433-455); the library is constructed from immature human PBMC, therefore the candidate antibodies have low affinity (Edwards B M, et al., The remarkable flexibility of the human antibody repertoire; isolation of over one thousand different antibodies to a single protein, BLyS. J Mol Biol. 2003 Nov. 14; 334(1):103-18); in most cases, the candidate medicaments from phage display library have drawbacks of low yield, low stability and poor pharmacokinetic character in vivo (Ponsel D, et al., High affinity, developability and functional size: the holy grail of combinatorial antibody library generation. Molecules. 2011 May 3; 16(5):3675-700).
Anti-BLyS antibodies with the following properties are still needed in the art: they are produced by, for example, using humanized mouse antibody technology, etc, without using phage display library; they are able to bind to B lymphocyte stimulator with high affinity and inhibit the B lymphocyte stimulator from binding to its receptor BR3-Fc, with high specificity; they have low immunogenicity; and/or they have low affinity with MHC II factor, thereby minimizing the immune response while ensuring affinity.